One conventional method used to produce molded metal alloys is the die cast method. In this method, the metal to be injected is heated above its liquidus temperature and then forced into the mold by the extension of a piston in the injection chamber. Another conventional method is the thixotropic injection molding method. In this method, the metal is first heated to a thixotropic state rather than to a completely liquid state, and then injected into a mold from an injection chamber. In this method, a screw rather than a piston is often used to inject the metal into the mold. The piston and the screw contain a shaft portion, which is attached to a drive mechanism. The drive mechanism is typically a motor, however, hydraulic mechanisms have also been used.
Although conventional liquid metal injection molding and thixotropic metal injection molding have been used successfully in the past, conventional machines suffer from metal leaking backwards past the piston or screw into the drive mechanism, rather than being injected forward into the mold. This occurs because high pressure is required to force the metal completely into the mold and it impossible to manufacture an apparatus without some clearance between the piston or screw and the inner wall of the injection chamber. Thus, the metal is forced past the piston or screw into the shaft housing. Some of this metal may reach the driving mechanism of the piston or screw and damage it. Thus, a device reducing the leakage of metal to the rear of the shaft housing in the injection molding of liquid and thixotropic metals is desired.